U.S. patent application number 12/811896 was filed with the patent office on 2010-11-04 for apparatus for treating radioactive nitrate waste liquid.
This patent application is currently assigned to MITSUBISHI HEAVY INDUSTRIES, LTD.. Invention is credited to Kazuhiko Kuroda, Hiromitsu Nagayasu, Naoki Ogawa, Katsushi Shibata.
Application Number | 20100276345 12/811896 |
Document ID | / |
Family ID | 40952277 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100276345 |
Kind Code |
A1 |
Ogawa; Naoki ; et
al. |
November 4, 2010 |
APPARATUS FOR TREATING RADIOACTIVE NITRATE WASTE LIQUID
Abstract
An apparatus for treating a radioactive nitrate waste liquid
includes: a denitrification tank (12) that accommodates active
sludge which adsorbs or takes in a radioactive substance in a
nitrate waste liquid (11) containing nitrate and the radioactive
substance and in which an anaerobic microorganism that reduces the
nitrate to nitrogen gas grows; a reaeration tank (14) that aerates
and mixes a denitrification-treated liquid (24) treated in the
denitrification tank (12) with the active sludge in which the
aerobic microorganism grows; and a sludge dissolution tank (81)
that dissolves redundant sludge (26A, 26B) discharged from the
denitrification tank (12) and the reaeration tank (14). Acetic
peracid (80) is supplied to the sludge dissolution tank (81) to
dissolve redundant sludge, a sludge lysate is supplied to the
denitrification tank (12) as a carbon source (22), and acetic acid
is supplied to the denitrification tank (12).
Inventors: |
Ogawa; Naoki; (Hyogo,
JP) ; Shibata; Katsushi; (Hyogo, JP) ; Kuroda;
Kazuhiko; (Tokyo, JP) ; Nagayasu; Hiromitsu;
(Hyogo, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
MITSUBISHI HEAVY INDUSTRIES,
LTD.
Minato-ku, Tokyo
JP
|
Family ID: |
40952277 |
Appl. No.: |
12/811896 |
Filed: |
February 6, 2009 |
PCT Filed: |
February 6, 2009 |
PCT NO: |
PCT/JP2009/052097 |
371 Date: |
July 7, 2010 |
Current U.S.
Class: |
210/85 ; 210/150;
210/151; 210/96.1 |
Current CPC
Class: |
B01D 61/14 20130101;
C02F 3/2853 20130101; C02F 1/66 20130101; B01D 2315/06 20130101;
G21F 9/18 20130101; C02F 2101/006 20130101; C02F 3/305 20130101;
B01D 61/58 20130101; C02F 3/34 20130101 |
Class at
Publication: |
210/85 ; 210/150;
210/151; 210/96.1 |
International
Class: |
G21F 9/18 20060101
G21F009/18; G21F 9/04 20060101 G21F009/04; C02F 3/30 20060101
C02F003/30; C02F 11/00 20060101 C02F011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2008 |
JP |
2008-029554 |
Claims
1. An apparatus for treating a radioactive nitrate waste liquid,
comprising: a denitrification tank that accommodates active sludge
which adsorbs or takes in a radioactive substance in a nitrate
waste liquid containing nitrate and the radioactive substance and
in which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank,
wherein a sludge solvent is supplied to the sludge dissolution tank
to dissolve redundant sludge, and a sludge lysate is supplied to
the denitrification tank as a carbon source.
2. The apparatus for treating a radioactive nitrate waste liquid
according to claim 1, wherein the sludge solvent is acetic peracid
or a nitrate waste liquid of which pH is equal to or more than
12.
3. An apparatus for treating a radioactive nitrate waste liquid,
comprising: a denitrification tank that accommodates active sludge
which adsorbs or takes in a radioactive substance in a nitrate
waste liquid containing nitrate and the radioactive substance and
in which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank,
wherein acetic peracid is supplied to the sludge dissolution tank
to dissolve redundant sludge, a sludge lysate is supplied to the
denitrification tank as a carbon source, and acetic acid is
supplied to the denitrification tank.
4. An apparatus for treating a radioactive nitrate waste liquid,
comprising: a denitrification tank that accommodates active sludge
which adsorbs or takes in a radioactive substance in a nitrate
waste liquid containing nitrate and the radioactive substance and
in which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank,
wherein a nitrate waste liquid of which pH is equal to or more than
12 is supplied to the sludge dissolution tank to dissolve redundant
sludge, a sludge lysate is supplied to the denitrification tank as
a carbon source, and a nitrate waste liquid is supplied to the
denitrification tank.
5. The apparatus for treating a radioactive nitrate waste liquid
according to claim 1, wherein the denitrification tank comprises: a
pH adjusting unit that supplies a pH adjuster used for adjusting pH
of the nitrate waste liquid; a first solid-liquid separating unit
that separates a denitrified liquid treated with the active sludge
into a solid content containing sludge and a
denitrification-treated liquid; and a gas supplying unit that is
arranged on a lower side of the first solid-liquid separating unit
and supplies gas not containing oxygen into the denitrification
tank, and the reaeration tank comprises: a second solid-liquid
separating unit that further separates the denitrification-treated
liquid treated with the active sludge into redundant sludge and a
treated liquid; and an air supplying unit that is arranged on a
lower side of the second solid-liquid separating unit and supplies
air into the reaeration tank.
6. The apparatus for treating a radioactive nitrate waste liquid
according to claim 1, wherein pH of the denitrified liquid in the
denitrification tank is from 7.0 to 10.0.
7. The apparatus for treating a radioactive nitrate waste liquid
according to claim 1, wherein the denitrification tank includes a
gas circulating line through which nitrogen gas and carbon dioxide
gas produced by a reaction between the aerobic microorganism and
the nitrate in the denitrified liquid are circulated into the
denitrification tank.
8. The apparatus for treating a radioactive nitrate waste liquid
according to claim 5, wherein the first solid-liquid separating
unit and the second solid-liquid separating unit are solid-liquid
separating films.
9. The apparatus for treating a radioactive nitrate waste liquid
according to claim 4, further comprising: a total-organic-carbon
measuring device that analyzes organic carbon in a nitrate waste
liquid discharged from the sludge dissolution tank, and a
total-nitrogen measuring device that measures an amount of nitrogen
in a nitrogen compound in a nitrate waste liquid discharged from
the sludge dissolution tank.
10. The apparatus for treating a radioactive nitrate waste liquid
according to claim 1, comprising an adjusting tank at an upstream
of the denitrification tank, wherein the adjusting tank comprises:
an electrical conductivity (EC) meter that measures a level of
electric conductivity; an industrial-water introducing line; and an
industrial-water supply-amount adjusting valve that is interposed
through the industrial-water introducing line and adjusts an
industrial-water supply amount based on a measurement value of the
electrical conductivity meter.
Description
TECHNICAL FIELD
[0001] The present invention relates to an apparatus for treating a
radioactive nitrate waste liquid capable of reducing nitrate
contained in waste water.
BACKGROUND ART
[0002] A nitrate waste liquid generated from nuclear facilities
such as a reprocessing plant has high concentration (salt
concentration of equal to or more than 1%) as well as being
radioactive. Therefore, the nitrate waste liquid cannot be
discharged as it is, and is finally cast into a cement-solidified
form and disposed underground.
[0003] In recent years, there has been a concern that when the
cement-solidified form contains nitrate, the nitrate may leak and
pollute surrounding ground water and soil environment and thus
dissolution of the nitrate is studied.
[0004] There are various methods for treating nitrate such as an
electric reduction method, a chemical reduction method, and a
biological reduction method. The electric reduction method has
problems such as inhibition by heavy metals and generation of
ammonia.
[0005] Besides, the chemical reduction method has problems such as
exothermic reaction and generation of ammonia.
[0006] On the other hand, the biological reduction method allows
treatment at an ordinary temperature and pressure and there is no
generation of ammonia.
[0007] Accordingly, the method of treating nitrate by using the
biological treatment has been studied (Patent Document 1). However,
in the method of Patent Document 1, only one type of carbon source
is used, so the method has problems such that the amount of
redundant sludge generated with the nitrate reduction treatment is
increased and a secondary waste disposal expense is increased.
[0008] FIG. 6 is a schematic diagram of a configuration of a
conventional apparatus for treating a radioactive nitrate waste
liquid utilizing an organism.
[0009] As shown in FIG. 6, a conventional apparatus 100 for
treating a radioactive nitrate waste liquid includes a
denitrification tank 102 that reduces nitrate, which is present in
a nitrate waste liquid 101 generated from nuclear facilities (not
shown), to nitrogen gas, a reaeration tank 104 that aerates and
mixes a denitrified liquid 103 obtained by denitrification with
active sludge, and a precipitation tank 108 that separates a
reaerated liquid 105 that is a denitrification-treated liquid
discharged from the reaeration tank 104 into precipitated sludge
106 and a treated liquid 107.
[0010] The denitrification tank 102 includes active sludge
containing a large amount of denitrifying bacteria (not shown). In
the denitrification tank 102, nitrate ions in a nitrate waste
liquid are reduced to nitrogen gas (N.sub.2) according to a
reaction based on the following formula (I) by an action of an
anaerobic microorganism (denitrifying bacteria) and is reduced from
the nitrate waste liquid.
[0011] At this time, a carbon source 121 such as methanol and a pH
adjuster 120 are supplied to the denitrification tank 102. Further,
a mixer 110 is used to mix inside the denitrification tank 102.
NO.sub.3.sup.-5/6CH.sub.3OH.fwdarw.1/2N.sub.2+5/6CO.sub.2+7/6H.sub.2O+OH-
.sup.- (1)
[0012] Thereafter, the reaerated liquid 105 passes through the
precipitation tank 108 from the reaeration tank 104, and is sent as
a treated liquid 107 to a subsequent process (not shown). The
sludge 106 precipitated in the precipitation tank 108 is recovered
as redundant sludge 131 by a circulating pump 111. Further, a part
of the sludge 106 precipitated in the precipitation tank 108 is
returned to the denitrification tank 102 via a returned-sludge
supplying line 112 and is reused. The sludge not reused is removed
from a system as the redundant sludge 131 and is sent to a
disposing process (not shown).
[0013] Further, there is used a method and an apparatus for
treating a nitrate-containing waste liquid. The method includes a
microbial treatment process of reducing nitrate nitrogen and
nitrite nitrogen to nitrogen by using anaerobic denitrifying
bacteria in microorganism-containing sludge, and the apparatus
includes a plurality of treatment tanks (Patent Document 2).
[0014] Patent Document 1: Japanese Patent No. 3697037
[0015] Patent Document 2: Japanese Patent Application Laid-open No.
2007-105627
DISCLOSURE OF INVENTION
Problem to be Solved by the Invention
[0016] However, in the conventional apparatus 100 for treating a
nitrate waste liquid, when the concentration of nitrate in the
nitrate waste liquid 101 is low (salt concentration is less than
1%), the denitrifying bacteria is not perished; however, when the
concentration of nitrate in the nitrate waste liquid 101 is high
(for example, about 1 to 7%), there is a problem that the
denitrifying bacteria may be perished due to a rise in pH with the
biological denitrification reaction.
[0017] Further, there is also the following problem. That is, when
the concentration of nitrate in the nitrate waste liquid 101 is
high (for example, about 1 to 7%), water seeps from a living
organism due to a rise in an osmotic pressure, its biology cannot
be maintained and the living organism is perished. Therefore, a
minute sludge floc is generated and the sludge 106 does not
precipitate in the precipitation tank 108, resulting in the sludge
106 flowing backwards with the treated liquid 107.
[0018] Still another problem is that, when the carbon source 121
supplied in the denitrification tank 102 (for example, organic acid
such as acetic acid or sweetener) is changed, there occurs a
multiplication of microorganisms, an increase in the generated
amount of redundant sludge 131, and an increase in the amount of
disposal.
[0019] There is also a problem for nuclear facilities that the
increased generated amount of the redundant sludge 131 leads to
huge expenses for disposal, because a secondary waste is disposed
underground as a solidified form. That is, there is a problem that
the amount of the secondary waste needs to be decreased.
[0020] Facilities that treat a radioactive nitrate waste liquid
need to be installed within a controlled area for radiation, and
thus there is a demand for making the treatment facilities
compact.
[0021] In addition, there is a demand that the amount of secondary
waste needs to be reduced.
[0022] Furthermore, as a microbial treatment system to be installed
within a controlled area for radiation, there is a demand that it
is needed to stabilize reactions and performances.
[0023] In view of the above problems, an object of the present
invention is to provide an apparatus for treating a radioactive
nitrate waste liquid, which is installed within a controlled area
for radiation and is capable of effectively microbially treating a
waste liquid with a high nitrate concentration.
Means for Solving Problem
[0024] According to an aspect of the present invention, an
apparatus for treating a radioactive nitrate waste liquid includes:
a denitrification tank that accommodates active sludge which
adsorbs or takes in a radioactive substance in a nitrate waste
liquid containing nitrate and the radioactive substance and in
which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank. A
sludge solvent is supplied to the sludge dissolution tank to
dissolve redundant sludge, and a sludge lysate is supplied to the
denitrification tank as a carbon source.
[0025] Advantageously, in the apparatus for treating a radioactive
nitrate waste liquid, the sludge solvent is acetic peracid or a
nitrate waste liquid of which pH is equal to or more than 12.
[0026] According to another aspect of the present invention, an
apparatus for treating a radioactive nitrate waste liquid includes:
a denitrification tank that accommodates active sludge which
adsorbs or takes in a radioactive substance in a nitrate waste
liquid containing nitrate and the radioactive substance and in
which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank.
Acetic peracid is supplied to the sludge dissolution tank to
dissolve redundant sludge, a sludge lysate is supplied to the
denitrification tank as a carbon source, and acetic acid is
supplied to the denitrification tank.
[0027] According to still another aspect of the present invention,
an apparatus for treating a radioactive nitrate waste liquid
includes: a denitrification tank that accommodates active sludge
which adsorbs or takes in a radioactive substance in a nitrate
waste liquid containing nitrate and the radioactive substance and
in which an anaerobic microorganism that reduces the nitrate to
nitrogen gas grows; a reaeration tank that aerates and mixes a
denitrification-treated liquid treated in the denitrification tank
with the active sludge in which the aerobic microorganism grows;
and a sludge dissolution tank that dissolves redundant sludge
discharged from the denitrification tank and the reaeration tank. A
nitrate waste liquid of which pH is equal to or more than 12 is
supplied to the sludge dissolution tank to dissolve redundant
sludge, a sludge lysate is supplied to the denitrification tank as
a carbon source, and a nitrate waste liquid is supplied to the
denitrification tank.
[0028] Advantageously, in the apparatus for treating a radioactive
nitrate waste liquid, the denitrification tank includes: a pH
adjusting unit that supplies a pH adjuster used for adjusting pH of
the nitrate waste liquid; a first solid-liquid separating unit that
separates a denitrified liquid treated with the active sludge into
a solid content containing sludge and a denitrification-treated
liquid; and a gas supplying unit that is arranged on a lower side
of the first solid-liquid separating unit and supplies gas not
containing oxygen into the denitrification tank, and the reaeration
tank includes: a second solid-liquid separating unit that further
separates the denitrification-treated liquid treated with the
active sludge into redundant sludge and a treated liquid; and an
air supplying unit that is arranged on a lower side of the second
solid-liquid separating unit and supplies air into the reaeration
tank.
[0029] Advantageously, in the apparatus for treating a radioactive
nitrate waste liquid, pH of the denitrified liquid in the
denitrification tank is from 7.0 to 10.0.
[0030] Advantageously, in the apparatus for treating a radioactive
nitrate waste liquid, the denitrification tank includes a gas
circulating line through which nitrogen gas and carbon dioxide gas
produced by a reaction between the aerobic microorganism and the
nitrate in the denitrified liquid are circulated into the
denitrification tank.
[0031] Advantageously, in the apparatus for treating a radioactive
nitrate waste liquid, the first solid-liquid separating unit and
the second solid-liquid separating unit are solid-liquid separating
films.
[0032] Advantageously, the apparatus for treating a radioactive
nitrate waste liquid further includes a total-organic-carbon
measuring device that analyzes organic carbon in a nitrate waste
liquid discharged from the sludge dissolution tank, and a
total-nitrogen measuring device that measures an amount of nitrogen
in a nitrogen compound in a nitrate waste liquid discharged from
the sludge dissolution tank.
[0033] Advantageously, the apparatus for treating a radioactive
nitrate waste liquid includes: an adjusting tank at an upstream of
the denitrification tank. The adjusting tank includes: an
electrical conductivity (EC) meter that measures a level of
electric conductivity; an industrial-water introducing line; and an
industrial-water supply-amount adjusting valve that is interposed
through the industrial-water introducing line and adjusts an
industrial-water supply amount based on a measurement value of the
electrical conductivity meter.
EFFECT OF THE INVENTION
[0034] According to the present invention, a part of redundant
sludge is supplied to a sludge dissolution tank, and the supplied
sludge is decomposed by using acetic peracid or the like as a
sludge solvent. Because a multiplied microorganism is perished and
the perished microorganism is an organic substance, the decomposed
material can be used as a carbon source that is supplied to a
denitrification tank.
[0035] Further, the present invention includes a first solid-liquid
separating unit that separates a denitrified liquid treated with
active sludge in a denitrification tank into a sludge-containing
solid content and a denitrification-treated liquid, and a second
solid-liquid separating unit that further separates a reaerated
liquid treated in a reaeration tank into a sludge-containing solid
content and a reaeration-treated liquid. Therefore, minute sludge
can be prevented from flowing out with a treated liquid.
BRIEF DESCRIPTION OF DRAWINGS
[0036] FIG. 1 is a conceptual diagram of an apparatus for treating
a radioactive nitrate waste liquid according to a first embodiment
of the present invention.
[0037] FIG. 2 is a schematic diagram of a configuration of an
apparatus for treating a radioactive nitrate waste liquid according
to a second embodiment of the present invention.
[0038] FIG. 3 is a schematic diagram of a configuration of an
apparatus for treating a radioactive nitrate waste liquid according
to a third embodiment of the present invention.
[0039] FIG. 4 is a schematic diagram of a configuration of an
apparatus for treating a radioactive nitrate waste liquid according
to a fourth embodiment of the present invention.
[0040] FIG. 5 is a schematic diagram of a configuration of a
biological treatment system using an apparatus for treating a
radioactive nitrate waste liquid according to a fifth embodiment of
the present invention.
[0041] FIG. 6 is a schematic diagram of a configuration of a
conventional apparatus for treating a radioactive nitrate waste
liquid utilizing an organism.
EXPLANATIONS OF LETTERS OR NUMERALS
[0042] 10A to 10D apparatus for treating radioactive nitrate waste
liquid [0043] 11 nitrate waste liquid [0044] 12 denitrification
tank [0045] 14 reaeration tank [0046] 21 pH adjuster [0047] 22
carbon source [0048] 23 denitrified liquid [0049] 24
denitrification-treated liquid [0050] 25 first solid-liquid
separating film [0051] 26A, 26B solid content (redundant sludge)
[0052] 27 reaeration-treated liquid [0053] 28 second solid-liquid
separating film [0054] 29 reaerated liquid [0055] 30 gas supplying
unit [0056] 31 gas discharge line [0057] 34 air supplying unit
[0058] 35 blower [0059] 51 adjusting tank [0060] 52 electrical
conductivity meter (EC meter) [0061] 53 industrial-water
introducing line [0062] 54 industrial-water supply-amount adjusting
valve [0063] 55 nitrate-waste-liquid supplying line [0064] 61
industrial water [0065] 62 diluter [0066] 63 biological treatment
device [0067] 65 sludge [0068] 67 sludge dewatering device [0069]
68 dewatered sludge [0070] 69 incinerator [0071] 70 treated liquid
[0072] 71 incinerated ashes [0073] 72 cleansing water [0074] 81
sludge dissolution tank
BEST MODE(S) FOR CARRYING OUT THE INVENTION
[0075] Exemplary embodiments of the present invention will be
explained below in detail with reference to the accompanying
drawings. Note that the present invention is not limited to the
embodiments. In addition, constituent elements in the embodiments
include those that can be easily assumed by those skilled in the
art or that are substantially equivalent.
First Embodiment
[0076] An apparatus for treating a radioactive nitrate waste liquid
according to an embodiment of the present invention is explained
with reference to the drawings.
[0077] FIG. 1 is a conceptual diagram of the apparatus for treating
a radioactive nitrate waste liquid according to a first embodiment
of the present invention.
[0078] As shown in FIG. 1, an apparatus 10A for treating a
radioactive nitrate waste liquid according to the present
embodiment is an apparatus for treating a radioactive nitrate waste
liquid that includes a denitrification tank 12 which accommodates
active sludge that adsorbs or takes in a radioactive substance in a
nitrate waste liquid 11 containing nitrate and the radioactive
substance and in which an anaerobic microorganism that reduces the
nitrate to nitrogen gas grows, and a reaeration tank 14 that
aerates and mixes a denitrification-treated liquid 24 treated in
the denitrification tank 12 with the active sludge in which an
aerobic microorganism grows. The apparatus 10A includes a sludge
dissolution tank 81 that dissolves redundant sludge 26A and 26B
discharged from the denitrification tank 12 and the reaeration tank
14. In the apparatus 10A, acetic peracid 80 is supplied as a sludge
solvent to the sludge dissolution tank 81 thereby to dissolve the
redundant sludge, and a sludge lysate is supplied as a carbon
source 22 to the denitrification tank 12.
[0079] The denitrification tank 12 includes a pH adjusting unit
(not shown) that supplies a pH adjuster 21 used for adjusting pH of
the nitrate waste liquid 11, a carbon-source supplying unit (not
shown) that supplies the carbon source 22 to the denitrification
tank 12, a first solid-liquid separating film 25 as a first
solid-liquid separating unit that separates a denitrified liquid 23
treated with the active sludge into a solid content containing the
sludge (the redundant sludge 26A) and a treated liquid, and a gas
supplying unit 30 that is arranged on a lower side of the first
solid-liquid separating film 25 and supplies gas not containing
oxygen (for example, one or both of nitrogen gas (N.sub.2) and
carbon dioxide gas (CO.sub.2)) into the denitrification tank 12.
The reaeration tank 14 includes a second solid-liquid separating
film 28 that reaerates the denitrification-treated liquid 24
treated with the active sludge to further separate a reaerated
liquid 29 into the redundant sludge 26B and a reaeration-treated
liquid 27, and an air supplying unit 34 that is arranged on a lower
side of the second solid-liquid separating film 28 as a second
solid-liquid separating unit and uses a blower 35 to supply air
into the reaeration tank 14.
[0080] At a lower portion of the first solid-liquid separating film
25 and the second solid-liquid separating film 28, the gas
supplying unit 30 and the air supplying unit 34 are arranged,
respectively. When the supplied gas rises, a liquid mixed with the
active sludge passes through surfaces of the separating films, and
at this time, the liquid only permeates the films, and a
solid-liquid separation is performed in this way. The active sludge
that is left after the separation adheres to the film surface;
however, the film surface is always cleansed with a flow of the
supplied gas. As a result, the active sludge that adheres to the
film surface is cleansed and reduced. This makes it possible to
perform a solid-liquid separation by using the film surface that is
always clean. In FIG. 1, reference character P.sub.1 denotes a
denitrification-treated-liquid supplying pump that supplies the
denitrification-treated liquid 24 to the reaeration tank 14 and
reference character P.sub.2 denotes a reaeration-treated-liquid
supplying pump that sends the reaeration-treated liquid 27.
[0081] In the present embodiment, parts of the redundant sludge 26A
and 26B from the denitrification tank 12 and the reaeration tank 14
are supplied to the sludge dissolution tank 81 through a
redundant-sludge supplying line L.sub.1, and by using the acetic
peracid 80 as the sludge solvent, the supplied parts are decomposed
in the tank 81. Because the multiplied microorganism is perished
and the perished microorganism is an organic substance, the
decomposed material can be used as the carbon source 22 that is
supplied to the denitrification tank 12 through a supplying pump
P.sub.3.
[0082] As the sludge solvent, the acetic peracid 80 is used, and
thus, as a result of the decomposition, acetic acid is produced.
The produced acid also is used as the carbon source 22, and
therefore this eliminates necessity of additional carbon source or
reduces addition of the carbon source.
[0083] That is, a material that originally contributes to a
denitrification reaction can be obtained from the redundant sludge.
Thus, in addition to a fact that the acetic peracid 80 is used for
dissolution of the redundant sludge, the organic substance from the
decomposed material and the acetic acid can be used as the carbon
source 22 for the denitrification tank 12. Therefore, an effective
utilization is achieved.
[0084] To perish the microorganism, substances such as chlorine and
ozone can be used besides the acetic peracid. However, although
these substances contribute to dissolution of the redundant sludge,
they cannot be supplied to the denitrification tank after the
dissolution and cause only adverse effects. Therefore, these
substances are not preferable.
[0085] After the dissolution, the redundant sludge is re-used as
the carbon source, and emitted as carbon dioxide gas. As a result,
it is possible to decrease the generated amount of secondary
waste.
[0086] Further, in the apparatus 10A for treating a radioactive
nitrate waste liquid according to the present embodiment, the first
solid-liquid separating film 25 and the second solid-liquid
separating film 27 are respectively arranged in the denitrification
tank 12 and the reaeration tank 14. Accordingly, the minute sludge
can be completely separated into the denitrified liquid 23 or the
reaerated liquid 29. This can prevent the sludge from flowing out.
Although not limited thereto, examples of types of the first
solid-liquid separating film 25 and the second solid-liquid
separating film 28 include well-known solid-liquid separating films
such as a flat film and a hollow fiber film.
[0087] As a result, when the minute sludge is completely separated
from the denitrification-treated liquid 24 or the
reaeration-treated liquid 27, it is possible to decrease the
concentration of suspended solid (SS) of the discharged
reaeration-treated liquid 27.
[0088] When the first solid-liquid separating film 25 is installed
within the denitrification tank 12, it is possible to prevent
denitrifying bacteria from flowing out, and there is no
contamination of any other bacteria. Thus, only a large amount of
denitrifying bacteria multiplied within the denitrification tank 12
exist in the tank. As a result, a sufficient amount of sludge can
be secured, and the sludge concentration within the denitrification
tank 12 can be maintained at a high level. Accordingly, a
high-level denitrification performance of the denitrification tank
12 can be maintained and the apparatus can be made compact.
[0089] A high concentration level of the sludge within the
denitrification tank 12 can be maintained, and thus the
denitrification performance of the denitrification tank 12 can be
enhanced and the apparatus can be made compact.
[0090] When the first solid-liquid separating film 25 and the
second solid-liquid separating film 27 are arranged, a particulate
radioactive substance contained in the nitrate waste liquid 11 can
be also separated from the reaeration liquid 29. Thus, it is
possible to decrease the radioactive concentration of the
reaeration-treated liquid 27 discharged to outside and to decrease
the radioactive concentration of the reaeration-treated liquid
27.
[0091] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, the pH of the
denitrified liquid 23 in the denitrification tank 12 is preferably
adjusted from 7.0 to 10.0. It is preferable that the pH is from 8.0
to 9.5, and more preferably the pH is 8.0 to 9.0. This is because
when the pH of the denitrified liquid 23 exceeds 10.0, the
microorganism is perished. Moreover, when the pH is less than 7.0,
a reaction rate for a treatment for reducing the nitrogen gas in
the microorganism is decreased.
[0092] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, the gas supplying
unit 30 is arranged on a lower side (bottom surface side of the
tank) of the first solid-liquid separating film 25 of the
denitrification tank 12 so as to supply gas not containing oxygen
(for example, nitrogen gas) to the denitrified liquid 23 of the
denitrification tank 12. This is because when there is oxygen in
the nitrate waste liquid 11, the reaction in the process for
reducing nitrogen gas in the anaerobic microorganism is not
progressed preferably.
[0093] By supplying nitrogen gas into the denitrified liquid 23 in
the denitrification tank 12 via the gas supplying unit 30, the
denitrified liquid 23 in the denitrification tank 12 can be
forcedly stirred and the treatment for reducing the nitrogen gas by
the microorganisms can be accelerated. Moreover, when nitrogen gas
is supplied via the gas supplying unit 30 from below the first
solid-liquid separating film 25, the active sludge that adheres to
the first solid-liquid separating film 25 can be reduced. As a
result, due to a gas cleansing effect, clogging of the film can be
prevented.
[0094] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, nitrogen gas
(N.sub.2 gas) is supplied by the gas supplying unit. However, the
present invention is not limited thereto, and any gas that does not
contain oxygen, such as carbon dioxide gas (CO.sub.2 gas) and an
inactive gas, can be used.
[0095] Further, in the apparatus 10A for treating a radioactive
nitrate waste liquid according to the present embodiment, nitrogen
gas (N.sub.2) and carbon dioxide gas (CO.sub.2) generated in the
denitrification tank 12 are released to outside via a gas discharge
line 31A.
[0096] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, initially, the
sludge used in sewage sludge or an industrial waste treatment is
put in as seed sludge and active sludge multiplied until the active
sludge concentration reaches, for example, about 5,000 to 20,000
mg/L, can be used. While the active sludge can be held by a
granular carrier or a fibrous carrier, in the exemplary embodiments
of the present invention, various types of such carriers are not
used, and floating active sludge is preferably used.
[0097] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, the decomposed
material obtained from the redundant sludge can be used as the
carbon source 22. When the carbon source 22 is separately supplied
from outside, although the present invention is not limited
thereto, organic acid can be used as the carbon source 22.
[0098] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, although the
present invention is not limited thereto, examples of the pH
adjuster 21 include sulfuric acid and hydrochloric acid.
[0099] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, as the
microorganism contained in the active sludge in the denitrification
tank 12, a well-known anaerobic microorganism that exhibits a
denitrification performance can be used. Although not particularly
limited thereto, in the reaeration tank 14, a well-known aerobic
microorganism for a reaeration can be used.
[0100] In the apparatus 10A for treating a radioactive nitrate
waste liquid according to the present embodiment, the solid-liquid
separating film is used as a solid-liquid separating unit; however,
the present invention is not limited thereto, and any unit that can
separate the sludge and the liquid can be used.
[0101] As described above, in the apparatus 10A for treating a
radioactive nitrate waste liquid according to the present
embodiment, parts of the redundant sludge 26A and 26B are supplied
to the sludge dissolution tank 81, and by using the acetic peracid
80 as a sludge solvent, the supplied sludge is decomposed in the
tank 81. Because the multiplied microorganism is perished and the
perished microorganism is an organic substance, the decomposed
material can be used as the carbon source 22 that is supplied to
the denitrification tank 12.
[0102] The acetic peracid 80 is used as a sludge solvent and, as a
result of the decomposition, acetic acid is produced. The produced
acetic acid also becomes the carbon source 22, and therefore this
eliminates necessity of additional carbon source or reduces
addition of the carbon source.
[0103] Furthermore, the first solid-liquid separating film 25 and
the second solid-liquid separating film 28 are respectively
arranged in the denitrification tank 12 and the reaeration tank 14.
Accordingly, the minute sludge can be completely separated into the
denitrification-treated liquid 24 and the reaeration-treated liquid
27. Thus, the sludge can be prevented from flowing out. Moreover,
the concentration of suspended solid (SS) in the reaeration-treated
liquid 27 that is discharged from the reaeration tank 14 and is
separately treated can be improved.
[0104] Because a sufficient amount of sludge can be secured within
the denitrification tank 12, the sludge concentration within the
denitrification tank 12 can be maintained at a high level.
Therefore, a high-level denitrification performance of the
denitrification tank 12 can be maintained and the apparatus can be
made compact.
[0105] In the denitrification tank 12, a gas circulating line (not
shown) through which the nitrogen gas (N.sub.2) and the carbon
dioxide gas (CO.sub.2) produced as a result of a reaction between
the anaerobic microorganism and the nitrate in the denitrified
liquid 23 are circulated within the denitrification tank 12 is
arranged and branched from a part of the gas discharge line 31.
[0106] As a result, the nitrogen gas (N.sub.2) and the carbon
dioxide gas (CO.sub.2) generated in the denitrification tank 12 are
fed to the gas supplying unit 30 by using a blower interposed
through a gas circulating line, and can be introduced into the
denitrification tank 12.
[0107] In this way, the nitrogen gas (N.sub.2) and the carbon
dioxide gas (CO.sub.2) generated as a result of the microorganism
reaction within the denitrification tank 12 are re-circulated and
re-used within the denitrification tank. Therefore, there is no
need to separately arrange the nitrogen gas supplying unit (as
shown in FIG. 1) that supplies gas not containing oxygen. As a
result, it is possible to eliminate the nitrogen gas supplying unit
and to reduce gas purchasing costs.
Test Example
[0108] By using the apparatus according to the present embodiment,
a denitrification test was conducted on a nitrate waste liquid
having an undiluted nitrate nitrogen concentration of 6700 to 9200
mg/L (salt concentration: 4.0 to 5.5%) by using methanol and acetic
acid as a carbon source with a test temperature set to 20 to
25.degree. C. (room temperature).
[0109] When the first solid-liquid separating film was not arranged
in the denitrification tank, the denitrification performance
reached 2 kg-N/m/d, whereas when the first solid-liquid separating
film was arranged in the denitrification tank, the denitrification
performance was improved to 7 kg-N/m/d.
[0110] While the denitrification performance of 7 kg-N/m/d when the
first solid-liquid separating film was arranged in the
denitrification tank was maintained, the generated amount of
redundant sludge was reduced to below 2/3 and an amount of carbon
source to be added (acetic peracid+acetic acid) was reduced to
below 1/2.
Second Embodiment
[0111] An apparatus for treating a radioactive nitrate waste liquid
according to a second embodiment of the present invention is
explained with reference to FIG. 2.
[0112] An apparatus 10B for treating a radioactive nitrate waste
liquid according to the present embodiment is configured
substantially identical to the apparatus 10A for treating a
radioactive nitrate waste liquid according to the first embodiment
shown in FIG. 1, and thus like reference letters or numerals are
denoted to like constituent elements of the apparatus for treating
a radioactive nitrate waste liquid according to the first
embodiment shown in FIG. 1, and redundant explanations thereof will
be omitted.
[0113] FIG. 2 is a schematic diagram of a configuration of the
apparatus for treating a radioactive nitrate waste liquid according
to the second embodiment of the present invention. As shown in FIG.
2, the apparatus 10B for treating a radioactive nitrate waste
liquid according to the present embodiment is configured to use a
nitrate waste liquid (undiluted liquid) 83 having pH of equal to or
more than 12 as the sludge solvent added to the sludge dissolution
tank 81.
[0114] In the present embodiment, instead of acetic peracid, an
alkaline (pH is equal to or more than 12) nitrate waste liquid
(undiluted liquid) is used. Thus, the redundant sludge 26A and 26B
is dissolved under an alkaline condition and becomes a solution in
which an organic substance is dissolved. The solution is supplied
as the nitrate waste liquid 11 to the denitrification tank 12, and
the organic substance is utilized as the carbon source.
[0115] The nitrate waste liquid (undiluted liquid) 83 reduces its
pH as a result of the dissolution of the sludge dissolution tank
81. Accordingly, it is possible to reduce a usage amount of the pH
adjuster 21 added in the denitrification tank 12.
Third Embodiment
[0116] An apparatus for treating a radioactive nitrate waste liquid
according to a third embodiment of the present invention is
explained with reference to FIG. 3.
[0117] The apparatus for treating a radioactive nitrate waste
liquid according to the present embodiment is configured
substantially identical to the apparatus for treating a radioactive
nitrate waste liquid according to the first embodiment shown in
FIG. 1, and thus like reference numerals are denoted to like
constituent elements of the apparatus for treating a radioactive
nitrate waste liquid according to the first embodiment shown in
FIG. 1, and redundant explanations thereof will be omitted.
[0118] FIG. 3 is a schematic diagram of a configuration of the
apparatus for treating a radioactive nitrate waste liquid according
to the third embodiment of the present invention.
[0119] As shown in FIG. 3, an apparatus 10C for treating a
radioactive nitrate waste liquid according to the present
embodiment includes a total-organic-carbon measuring device (TOC)
84 that analyzes an organic carbon in the nitrate waste liquid 11
discharged from the sludge dissolution tank 81 and a total-nitrogen
measuring device (T-N) 85 that measures the amount of nitrogen in a
nitrogen compound in the nitrate waste liquid 11.
[0120] Based on this measurement result, the amount of the carbon
source 22 separately added to the denitrification tank 12 is
adjusted to increase or decrease so that the value of the TOC/T-N
is from 7.5 to 11 (in terms of C/N, 3.0 to 4.5).
[0121] Accordingly, there is no excessive supply of the excessive
carbon source 22 and an appropriate amount of the carbon source can
be supplied, and thus a stable denitrification reaction can be
performed.
[0122] Therefore, it becomes possible to decrease the amount of
carbon source to be added and also to decrease the generated amount
of secondary waste.
Fourth Embodiment
[0123] An apparatus for treating a radioactive nitrate waste liquid
according to a fourth embodiment of the present invention is
explained with reference to FIG. 4.
[0124] The apparatus for treating a radioactive nitrate waste
liquid according to the present embodiment is configured
substantially identical to the apparatus for treating a radioactive
nitrate waste liquid according to the first embodiment shown in
FIG. 1, and thus like reference letters or numerals are denoted to
like constituent elements of the apparatus for treating a
radioactive nitrate waste liquid according to the first embodiment
shown in FIG. 1, and redundant explanations thereof will be
omitted.
[0125] FIG. 4 is a schematic diagram of a configuration of the
apparatus for treating a radioactive nitrate waste liquid according
to the fourth embodiment of the present invention.
[0126] As shown in FIG. 4, in an apparatus 10D for treating a
radioactive nitrate waste liquid according to the present
embodiment, an adjusting tank 51 that supplies a nitrate waste
liquid (undiluted: salt concentration of 30 to 40%) 50 is arranged
at an upstream of the denitrification tank 12 of the apparatus 10A
for treating a radioactive nitrate waste liquid according to the
first embodiment shown in FIG. 1. The adjusting tank 51 includes an
electrical conductivity meter (EC meter) 52 that measures a level
of electric conductivity, an industrial-water introducing line 53,
and an industrial-water supply-amount adjusting valve 54 which is
arranged in the industrial-water introducing line 53 and which
adjusts a flow rate of water to be diluted based on a measurement
value of the electrical conductivity meter 52.
[0127] The industrial-water supply-amount adjusting valve 54
arranged in the industrial-water introducing line 53 is controlled
based on the EC value measured by the electrical conductivity meter
(EC meter) 52 arranged in the adjusting tank 51 to adjust the flow
rate of water supplied to the adjusting tank 51.
[0128] Specifically, when the EC value measured by the electrical
conductivity meter (EC meter) 52 is high, the industrial-water
supply-amount adjusting valve 54 is opened, and when the EC value
measured by the electrical conductivity meter (EC meter) 52 is low,
the industrial-water supply-amount adjusting valve 54 is
closed.
[0129] In the apparatus 10D for treating a radioactive nitrate
waste liquid according to the present embodiment, when a biological
treatment is performed in a high salt concentration state of about
4%, for example, by diluting the nitrate waste liquid (undiluted:
salt concentration of 30 to 40%), a control range of an EC value
measured by the electrical conductivity meter (EC meter) 52 at this
time is preferably from 50 to 70 mS/cm, and more preferably from 53
to 68 mS/cm.
[0130] In the apparatus 10D for treating a radioactive nitrate
waste liquid according to the present embodiment, a
nitrate-waste-liquid supplying pump P.sub.4 is arranged in a
nitrate-waste-liquid supplying line 55 that feeds the nitrate waste
liquid 50 (undiluted liquid) to the adjusting tank 51. Based on the
EC value measured by the electrical conductivity meter (EC meter)
52, the nitrate-waste-liquid supplying pump P.sub.4 is controlled,
and a supply amount of the nitrate waste liquid 50 (undiluted
liquid) to be fed to the adjusting tank 51 is thus adjusted.
[0131] Specifically, when the EC value measured by the electrical
conductivity meter (EC meter) 52 is high, the nitrate-waste-liquid
supplying pump P.sub.4 is stopped to halt supplying of the
undiluted nitrate waste liquid 50 to the adjusting tank 51, and
when the EC value measured by the electrical conductivity meter (EC
meter) 52 is low, the nitrate-waste-liquid supplying pump P.sub.4
is operated and the nitrate waste liquid 50 (undiluted liquid) is
supplied to the adjusting tank 51.
[0132] As a result, the concentration of a high-concentration
nitrate waste liquid from treatment facilities is not always
constant, and thus, even when the concentration of the nitrate
waste liquid (undiluted liquid) 50 is not constant, it is possible
to prevent transferring variation of the salt concentration in the
nitrate waste liquid (undiluted liquid) 50 to the denitrification
tank 12. This makes it possible to prevent a significant decrease
in denitrification performance caused when the salt concentration
is greatly varied.
[0133] Further, the nitrate waste liquid (diluted solution) 11 with
a constant salt concentration can be supplied to the
denitrification tank 12 via the nitrate-waste-liquid supplying pump
P.sub.5, and thus the denitrification performance can be
stabilized.
Fifth Embodiment
[0134] A biological treatment system using the apparatus for
treating a radioactive nitrate waste liquid according to a fifth
embodiment of the present invention is explained with reference to
FIG. 5.
[0135] As the apparatus for treating a radioactive nitrate waste
liquid according to the present embodiment, any one of the
apparatuses for treating a radioactive nitrate waste liquid
according to the first to fourth embodiments shown in FIGS. 1 to 4
can be used, and thus explanations thereof will be omitted.
[0136] As shown in FIG. 5, the biological treatment system 60
according to the present embodiment includes a diluter 62 that
dilutes the nitrate waste liquid (undiluted liquid) 50 with
industrial water 61, a biological treatment device (any one of the
apparatuses for treating a radioactive nitrate waste liquid
according to the first to fourth embodiments) 63 in which nitrate
ions in the diluted nitrate waste liquid 11 are microbially treated
for reduction with nitrogen and reaeration, a sludge dewatering
device 67 that separates sludge 65 and a treated liquid 70 from the
biologically treated liquid treated in the biological treatment
device 63 and dewaters the separated sludge 65, and an incinerator
69 that incinerates dewatered sludge 68.
[0137] The diluter 62 operates in the adjusting tank 51 that
dilutes an undiluted liquid as shown in FIG. 4 corresponding to the
fourth embodiment described above.
[0138] The biological treatment device 63 is an apparatus for
treating a radioactive nitrate waste liquid configured by the
denitrification tank 12 having the sludge dissolution tank 81 and
the reaeration tank 14.
[0139] The sludge dewatering device 67 dewaters the redundant
sludge discharged from the denitrification tank and the reaeration
tank of the biological treatment device 63. The incinerator 69
incinerates the dewatered sludge 68 or secondary waste discharged
from the sludge dewatering device 67 into incinerated ashes 71.
[0140] In the biological treatment device 63 that biologically
treats the nitrate waste liquid having a high salt concentration,
at the time of dewatering the redundant sludge, the salt
concentration in the water that adheres to the sludge is high, and
thus an amount of secondary waste (incinerated ashes) occasionally
increases. For this, in the redundant sludge dewatering device 67,
the industrial water 61 is added to flush the adhered liquid having
a high salt concentration, and flushed cleansing water 72 is used
as diluting water in the diluter 62 that dilutes the nitrate waste
liquid 11.
[0141] Therefore, a part of the industrial water 61 used in the
diluter 62 is used for cleansing at the time of dewatering, and
thus there is no need to use additional industrial water 61.
Further, by decreasing the salt concentration in the adhering
water, the amount of the secondary waste (incinerated ashes) can be
decreased to about 1/2.
INDUSTRIAL APPLICABILITY
[0142] As described above, by using the apparatus for treating a
radioactive nitrate waste liquid according to the present
invention, a waste liquid with a high nitrate concentration
discharged from nuclear facilities such as a reprocessing plant can
be microbially treated efficiently, and minute sludge can be
prevented from flowing out with a treated liquid.
* * * * *